Despite recent advances in early detection and treatment, breast cancer remains a common and significant health problem in the United States. Women diagnosed with stage II and III breast cancer have a high-risk for distant recurrence and up to half of these women will develop metastatic disease, which remains incurable with current therapy. In this setting, there is intense effort in the search for biomarkers that can detect early disease, and to monitor for disease progression and recurrence. With the advent of molecularly-targeted therapeutics, biomarkers that are associated with biological subtypes of cancer may be useful for predicting responses to therapeutic interventions.
Proteomics-based approaches to distinguish cancer-bearing patient sera from healthy control sera have been challenged by the difficulty in identifying small quantities of protein fragments within complex protein mixtures, protein instability, and natural variations in protein content within patient populations. Autoantibodies (AAb) to tumor antigens have advantages over other serum proteins as potential cancer biomarkers as they are stable, highly specific, easily purified from serum, and are readily detected with well-validated secondary reagents. Although they have high specificities to distinguish cancer from control sera, most tumor AAb demonstrate poor sensitivities. Testing multiple antigens in parallel may serve to increase the predictive value of tumor-specific antibodies for use as immunodiagnostics.
Protein microarrays offer an emerging platform to present tumor antigens to screen for immune responses. In comparison to traditional ELISAs, protein microarrays are capable of presenting and assessing hundreds of tumor antigens simultaneously. The responses are rapidly identified because the address of each protein is known in advance and there are no representation issues; all proteins, even rare ones, are represented equally (usually in duplicate). The proteins are arrayed on a single microscope slide requiring only a few microliters of serum per assay. Known tumor antigens as well as predicted tumor antigens can be included to generate a comprehensive protein tumor antigen array. Despite some early demonstrations of feasibility, protein microarrays are not yet widely used, due to the labor and technical issues associated with production, purification, and quality control of proteins for spotting on the array, as well as difficulties with downstream validation assays of target AAb.